02 July 2013

Study in scarlet

Almost every pond and flooded plain on the island is home to a population of Crocothemis servilia, a medium-large libellulid that is probably the most common red dragonfly in urban Singapore. The males are hard to miss; clad in scarlet from end to end save a dark stripe across the top of the abdomen, these insects are usually caught napping on emergent vegetation with their spiny legs gripping the edges of handy stalks or hanging blades. The veins at the base of the hindwings are stained with stingy amber. Females, which also boast a racing stripe, are as abundant as their mates but less easily spotted, as their pale brown bodies melt readily into a sea of reeds and cat-tails.

The same waterbodies may also harbour a few scarlet baskers, which can be told apart by the presence of two dark spots near the tip of the abdomen as well as markedly more angular wings. Urothemis signata also favours more prominent outposts, isolated perches on which males can survey their territory for rivals while aiming their tails at the sun. The slightly larger scarlet skimmer may vie with Crocothemis for choice spots, but Orthetrum testaceum is better described as orangey-red and lacks dorsal striping. Another candiate for confusion is Rhodothemis rufa, which can be distinguished by a pale dorsal band that illuminates a darker synthorax and eyes that meet, like opposing teardrops, at just one point.

With repeated observation, common scarlets betray a habitus that can be described as straight and stiff, as the abdomen is typically held with little deviation in alignment from the head and thorax. Only at the height of day, when ambient rays threaten to scorch the backs of already red-hot speedsters, do the dragonflies break formation and raise their bottoms, though with far less spirit than the baskers and flutterers in their midst that twirl themselves into Roman needles to pierce the noontime flame. In name, this species honours Servilia Caepionis, mother of Brutus and mistress of Julius Caesar, a noblewoman who oversaw bloodshed of Shakespearan proportions. Krokos, Greek for saffron, is thought to refer to the measly dab of yellow at the wingbases, while Themis is an avatar of order and the patron deity of odonate taxonomists.

At home in still waterbodies, rice paddies and marshy lowlands between Australasia and the Middle East, west of which lords its congener erythraea, servilia is a beast of open habitats, disturbed wetlands and suburban pools, a beauty of common places with no love for deep woods. Within isolated refugia such as Toa Payoh Park, the dragonflies occur in moderate densities, each individual seldom straying far from a circle of favoured perches, which may be shared with hunters of a different shade but not with similarly clad skimmers, who are pursued until one settles beyond the discomfort zone of the other.

The natural distribution of common scarlets may be explained by their high capacity for dispersal, but Crocothemis servilia has also crossed borders with a little help from unwitting friends. Since 1975, the species has colonised much of southern Florida, thanks no doubt to the state's thriving tropical fish industry and trade in exotic macrophytes from the Far East, where the eggs or nymphs of hardy dragonflies were probably deposited. Similar vectors are suspected with populations in Cuba and Hawaii; in the latter state, servilia was first spotted in Oahu in 1994 before spreading westwards to Kauai. These accidental introductions have had little perceptible impact on native andendemic odonates, though, which suffer more from the depredations of poecilids – guppies, mollies, swordtails and Gambusia – as their young have lost the ability to evade hungry fish. Adaptable, tolerant and vagile, Crocothemis servilia stands a far better chance of survival in waters that seldom stir but swarm with invaders from a hostile space that threaten to impose a blanket of continental values on outposts of fragile diversity.